Spontaneity and Entropy

Spontaneity

• Spontaneous processes do not require energy input
• Non-spontaneous processes need energy to occur

Entropy

• Entropy measures the disorder or randomness within a system
• A positive change in entropy means the final state is more random than the initial state
• Entropy depends on the state of disorder
• Reactions are more likely to happen if they increase disorder or entropy

Factors Influencing Entropy

• Entropy is affected by physical state, amount of substance, temperature, volume, pressure, and size
• Gases exhibit the greatest entropy due to molecular freedom

Entropy by Physical State

• Solids have the least entropy because they are highly ordered
• Liquids have greater entropy than solids; molecules are more disorderly, allowing limited movement

Entropy and Amount of Substance

• More substance generally means greater entropy
• Chemical reactions with more products than reactants tend to be spontaneous

Entropy and Temperature

• Higher temperatures increase entropy by increasing kinetic energy and particle freedom
• Lowering temperature decreases entropy; at absolute zero, entropy approaches zero

Entropy and Volume, Pressure, Size

• Increased volume leads to increased entropy
• Lower pressure leads to higher entropy
• Increased size leads to increased entropy

Spontaneity and Thermodynamics

• Enthalpy (H), Entropy (S) and Gibbs Free Energy (G) are key factors in spontaneity
• Enthalpy measures heat energy absorbed or released
• Entropy measures randomness, and Gibbs Free Energy measures available energy for chemical transformations

Second Law of Thermodynamics

• Any spontaneous process increases the universe's entropy

Gibbs Free Energy

• Gibbs Free Energy combines enthalpy and entropy to determine spontaneity
• At constant temperature and pressure, Gibbs Free Energy is defined using the Second Law of Thermodynamics
• Gibbs Free Energy measures the minimum work required to drive a spontaneous reaction

Gibbs Free Energy and Spontaneity

• ΔG < 0 indicates an exergonic, spontaneous reaction favoring products
• ΔG > 0 indicates an endergonic, non-spontaneous reaction favoring reactants
• ΔG = 0 indicates equilibrium; product and reactant concentrations remain constant

Entropy Changes

• (+) ΔS indicates an increase in randomness
• (-) ΔS indicates a decrease in randomness

Enthalpy Changes

• negative ΔH°f means energy is released (exothermic)
• positive ΔH°f means energy is absorbed (endothermic)

Equilibrium State

• Equilibrium represents a balanced state

Chemical Reactions

• Chemical reactions involve reactants forming products
• Reactions can be natural or synthetic

Reversible Reactions

• Reversible reactions, indicated by a double-headed arrow, occur spontaneously in both directions

Reversible Reaction Processes

• Forward reaction describes reactants forming products
• Reverse reaction describes products forming reactants

Chemical Reaction Balance

• A reaction's forward progress is balanced by its reverse progress

Law of Mass Action

• The Law of Mass Action/Equilibrium Constant relates reactant and product concentrations

Equilibrium Constant (K)

• K is the ratio of product to reactant concentrations at equilibrium, each raised to their stoichiometric coefficients
• K determines the "position" of equilibrium, predicting reaction direction and product formation extent

Equilibrium Constant Values

• A large equilibrium constant favors product formation
• A small equilibrium constant favors reactants

Le Chatelier's Principle

• If a system at equilibrium experiences stress, it shifts to relieve that stress
• Shifts can be caused by adding reactants (shifts forward to produce more products) or removing products (shifts forward to replace missing product)

Boyle's Law

• Changing volume or pressure affects equilibrium

Acids and Bases Importance

• Acids and Bases play a role in different environments
• Substances can be acidic, basic, or neutral based on ion concentrations

Acids

• Acids have a greater concentration of hydronium ions than hydroxide ions

Bases

• Bases have a lesser concentration of hydronium ions than hydroxide ions

Neutral Substances

• Neutral substances have equal concentrations of hydronium and hydroxide ions

Acid Properties

• Acids have a sour taste
• Acids turn litmus paper red
• Acids have a pH less than 7
• Acids react with active metals to produce hydrogen gas
• Acids can burn skin due to reactions with skin proteins and water
• Acids occur in solid, liquid, or gas forms

Base Properties

• Bases have a bitter taste
• Bases turn litmus paper blue
• Bases have a pH greater than 7
• Bases react with fats or oils to form soap and glycerol
• Bases feel slippery or soapy due to reactions with skin oils
• Bases occur in solid or liquid forms

Bronsted-Lowry Theory

• Describes acid-base interactions via PROTON TRANSFER
• A Bronsted-Lowry acid donates a proton (H⁺)
• A Bronsted-Lowry base accepts a proton (H⁺)

Acid-Base Pairs

• When an acid or base dissolves in water, a conjugate acid-base pair forms
• Monoprotic acids donate one H⁺
• Diprotic acids donate two H⁺
• Polyprotic acids donate three or more H⁺

Water Properties as Acid-Base

• Water is amphoteric, acting as both an acid and a base
• Water is a weak electrolyte that slightly ionizes into hydrogen and hydroxide ions

pH Measurement

• pH indicates acidity
• pH means "potential of hydrogen” or “power of hydrogen”
• pH was developed in 1909 by Soren Peter Lauritz Sorensen
• The body functions best within a pH of 7.0 to 7.8

pH Indicators

• Indicators determine if a solution is acidic or basic by changing color at the pH level
• Phenolphthalein is an indicator used in acid-base titrations, turning pink in basic solutions and is colorless in acidic solutions

Litmus Paper

• Litmus paper tests solution acidity or basicity
• Blue litmus paper turns red in acidic conditions
• Red litmus paper turns blue in basic or alkaline conditions

Natural Indicators

• Natural indicators, like FLAVIN, change colors with hydrogen ion concentration

Quantitative

• pH meters measure hydrogen ion concentration

Universal pH Indicator

• Universal pH indicators change into a range of colors and determine solution pH

Numeric pH Scale

• The pH scale specifies aqueous solution acidity or basicity

pH Values

• pH
• pOH > 7 indicates acidity
• pH = 0 and pOH - 0 indicates neutrality
• pH > 7 and pOH < 7 indicates basicity

Second Law of Thermodynamics

• Spontaneous processes include drying leaves, rusting iron, and radioactive decay
• Irreversible processes include preparing NaCl solutions, forming frost, and melting ice

Chemical Equilibrium

• Equilibrium is achieved when the amounts of added substances become stable
• Dissolving NaOH in water is exothermic, releasing heat and causing a temperature increase
• Exothermic reactions are spontaneous

Acids Bases Strengths

• Weak acids include acetic acid (CH₃COOH), carbonic acid (H₂CO₃), and hydrofluoric acid (HF)
• Weak bases include ammonia (NH₃), sodium bicarbonate (NaHCO₃), and lithium hydroxide (LiOH)

Strong Acids

• Strong acids include perchloric acid (HClO₄), sulfuric acid (H₂SO₄), and hydrochloric acid (HCl)

Metal Hydroxides

• Metal hydroxides include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂), lithium hydroxide (LiOH), and barium hydroxide (Ba(OH)₂)

Buffer Solutions

• Buffers maintain pH when small amounts of acids or bases are added
• Consist of a weak acid/conjugate base or weak base/conjugate acid pair
• Buffers play a role in bodily fluids